The present disclosure relates to semiconductor structures and particularly to metal electrical fuses that can be formed in a back-end-of-line (BEOL) interconnect structures and methods of programming the same.
Electrical fuses and electrical antifuses are used in the semiconductor industry to implement array redundancy, field programmable arrays, analog component trimming circuits, and chip identification circuits. Once programmed, the programmed state of an electrical fuse or an electrical antifuse does not revert to the original state on its own, that is, the programmed state of the fuse is not reversible. For this reason, electrical fuses and electrical antifuses are called One-Time-Programmable (OTP) memory elements.
FIG. 1 illustrates a circuit schematic of a circuitry including an electrically programmable fuse (“eFuse”) 1100. The electrically programmable fuse 1100 and a programming circuit 1200 are connected in a series connection between a power supply node Vdd and electrical ground. The programming circuit 1200 includes a switch, which can be implemented in the form of at least one transistor 1201 configured to switch on or off the electrical current through the electrically programmable fuse 1100. When a programming signal is applied to a programming node P, which can be the gate of a programming transistor 1201, electrical current passes through, and programs, the electrically programmable fuse 1100. An unprogrammed electrically programmable fuse has a low resistance, which is typically less than 100 Ohms, and a programmed electrically programmable fuse has a high resistance, which is typically greater than 1 kOhms. A sensing circuit 1300 attached to a node between the electrically programmable fuse 1100 and the programming circuit 1200 is configured to indicate the state of the electrically programmable fuse 1100 at the sense node S. The sensing circuit 1300 can include, for example, a sensing resistor 1301 connected in a parallel connection with the programming circuit 1200 relative to the electrically programmable fuse 1100. When the switch is turned off in the programming circuit 1200, for example, by turning off the programming transistor, the electrically programmable fuse 1100 and the sensing resistor 1301 can function as a voltage divider, thereby providing a voltage output at the sensing node S that depends on the state of the electrically programmable fuse 1100. Various sensing circuits 1300 are known in the art.
A metal electrically programmable fuse is formed in back-end-of-line (BEOL) interconnect structures, and thus, requires much less device area than a metal-silicide-based electrically programmable fuse. Challenges for metal eFuses include reliable programming yield and reproducibility. Ideally, programming of a metal eFuse should form a void in a metal line through electromigration of metal without causing damage to a liner or a dielectric cap or surrounding interlevel dielectric materials. However, controlling electromigration in a metal line has been very difficult, and programming of prior art metal fuses has produced a combination of voiding and fusing between metal line and a metallic liner, or an uncontrolled blow. If the programming power is too low, a void in a programmed metal fuse can be too small, and there is a possibility of “healing” of a programmed metal eFuse during product operation through metal electromigration, which can render a programmed fuse to be sensed as an unprogrammed fuse. If the programming power is too high, collateral structural damage to surrounding structures can be too extensive; impact to reliability of neighboring metal lines and introducing reliability concerns. In practice, due to structure to structure, chip to chip, wafer to wafer, and lot to lot variations in the physical structures for metal eFuses, the programming power window for prior art metal eFuses can be very small.